Braking mechanisms

ABSTRACT

A braking mechanism or &#39;&#39;&#39;&#39;hold back&#39;&#39;&#39;&#39; is disclosed including a rotatable drum; a strap substantially encircling the periphery of the drum; a lever movable about a fulcrum located in a zone intermediate its ends, one end of the lever being pivotally connected to one end of the strap and the other end of the lever being constrained for movement within a predetermined range; an operative connection whereby movement of the lever is transmitted to the other end of the strap; and a chamber housing the several elements and defining a bath for an oil type liquid; the arrangement being such that normal rotational movement of the drum in one direction acts through the liquid disposed between the drum and the strap to urge the strap to an open position in which it does not obstruct movement of the drum, while rotational movement of the drum in the reverse direction acts through the liquid to urge the lever to move about its fulcrum so as to draw the strap into firm braking engagement with the periphery of the drum. The strap preferably comprises two arcuate sections pivotally connected to each other with a pivotal connection being provided between the free extremity of the first strap section and one end of the lever and a pressure zone in which movement of the lever about its fulcrum in a direction to exert a braking force is transmitted to the free end of the second strap section to tighten the strap about the periphery of the drum.

llnited States Patent [1 1 Prins [451 Sept. 24, 1974 BRAKING MECHANISMS [76] Inventor: Christian F. Prins, PO. Box 4167,

Johannesburg, South Africa [22] Filed: Nov. 29, 1972 [21] Appl. No.: 310,241

[52] US. Cl. 188/826, 188/77 R [51] Int. Cl F16d 65/06 [58] Field of Search 188/77 R, 82.1, 82.6, 271,

Primary ExaminerDuane A. Reger Attorney, Agent, or Firm-Dike, Bronstein, Roberts, Cushman & Pfund [5 7 ABSTRACT A braking mechanism or hold back is disclosed including a rotatable drum; a strap substantially encircling the periphery of the drum; a lever movable about a fulcrum located in a zone intermediate its ends, one end of the lever being pivotally connected to one end of the strap and the other end of the lever being constrained for movement within a predetermined range; an operative connection whereby movement of the lever is transmitted to the other end of the strap; and a chamber housing the several elements and defining a bath for an oil type liquid; the arrangement being such that normal rotational movement of the drum in one direction acts through the liquid disposed between the drum and the strap to urge the strap to an open position in which it does not obstruct movement of the drum, while rotational movement of the drum in the reverse direction acts through the liquid to urge the lever to move about its fulcrum so as to draw the strap into firm braking engagement with the periphery of the drum. The strap preferably comprises two arcuate sections pivotally connected to each other with a pivotal connection being provided between the free extremity of the first strap section and one end of the lever and a pressure zone in which movement of the lever about its fulcrum in a direction to exert a braking force is transmitted to the free end of the second strap section to tighten the strap about the periphery of the drum.

3 Claims, 3 Drawing Figures PAIENIEB E MW 3.837.440

sum 1 or 2 THIS invention relates to braking mechanisms and is concerned with devices adapted to permit forward movement of a unit only and to restrain movement in the reverse direction. Such devices are commonly referred to as hold backs.

Several different types of hold back are known. Mention need only be made of the wellknown rack and pawl mechanism and the unit which relies upon line braking contacts being established between a rotatable drum and rollers spaced about the drum periphery, the rollers being trapped in circumferential slots between the drum and an outer sleeve-like housing. The draw back of the rack and pawl mechanism is that stripping of the rack teeth is possible under excessive loads and wear on both pawl and rack teeth can suddenly give rise to dangerous slip unless constant inspection is restored to. The roller type hold back has disadvantages in that in the braking disposition line contacts only are established between the rollers and the drum so that all the braking force is applied on an extremely small area of the drum periphery. In use, it is clear that the drum tends to corrugate axially and replacement rather than repair is generally necessary.

The object of the present invention is to provide a hold back device which the applicant believes will be efficient in use and superior in most respects to the devices referred to in the preceding paragraph.

According to the invention, a hold back device comprises a rotatable drum; a strap substantially encircling the periphery of the drum; a lever movable about a fulcrum located in a zone intermediate its ends, one end of the lever being pivotally connected to one end of the strap and the other end of the lever being con: strained for movement within a predetermined range; an operative connection whereby movement of the lever is transmitted to the other end of the strap; and a chamber housing the several elements and defining a bath for an oil type liquid; the arrangement being such that normal rotational movement of the drum in one direction acts through the liquid disposed between the drum and the strap to urge the strap to an open position in which it does not obstruct movement of the drum, while rotational movement of the drum in the reverse direction acts through the liquid to urge the lever to move about its fulcrum so as to draw the strap into firm braking engagement with the periphery of the drum.

Further according to the invention the device has a strap comprising a first arcuate section which embraces part of the drum periphery, and a second arcuate section which embraces another part of the drum periphery; a pivotal connection between the two strap sections; a pivotal connection between the free extremity of the first strap section and one end of the lever; and a pressure zone in which movement of the lever about its fulcrum in a direction to exert a braking force is transmitted to the free end of the second strap section to tighten the strap about the periphery of the drum.

Also according to the invention, theinternal drum engaging surfaces of the strap and/or the strap engaging surfaces of the drum may be formed with axially disposed grooves to permit the escape of liquid as braking engagement takes place.

The nature of the invention and the manner in which it is to be performed will be further described purely by way of example with reference to the accompanying drawings in which:

FIG. 1 is a part sectional elevation through one type of hold back in accordance with the invention;

FIG. 2 is a longitudinal elevation, partly in section, of

the drum used in the hold back,

FIG. 3 is an exploded perspective view of the strap used in the hold back."

Referring to the drawings, the hold back shown in the drawings has a drum 4 keyed to a shaft 5 and it employs a strap comprising a first section 6 and a second section 7. There is also a lever element 8.

The strap sections will be seen from FIG. 1 to be assembled in such a manner that the strap almost completely embraces the drum 4 with the lever 8 lying beneath the drum as shown. All the elements are housed within a casing 9 which defines a bath for a suitable oil.

The lever 8 is pivotally connected at one end 10 to the first strap section 6 by means of a pin 11. Strap sections 6 and 7 are pivotally connected to each other by a similar pin 12. The underface of the end 13 of the strap section 7 is grooved at 14 to accommodate part of the peripheral surface of a cylindrical pin which is split longitudinally into two halves, 15a and 15b. The portion 15a is received in the groove 14 and the other portion 15b is received in a groove 16 in the lever 8. One extremity of the portion 15b is secured in a semicircular slot 17 in a plate 18 which is fastened to the lever 8 by means of a bolt (not shown) passing through a hole 19 in the plate 18 into a threaded socket 20 in the lever 8.

A rod 21 extends vertically within the casing 9. It is threaded to receive nuts 22, 23 and 24 and a helical spring 25 is interposed between the nut 22 and a pressure washer 26. The nut 24 bears upon the upper surface of the end 27 of the lever 8 which is bifurcated at 28 to accommodate the rod 21. The lower end of the rod 21 is received in a hole in the base of the casing 9. A bifurcated lug 29 extends outwards from the strap section 7 and it embraces the rod 21 between the pres sure washer 26 and the nut 23. The upper end of the rod 21 carries a helical spring 30 and a securing nut 31. Adjustment in the relationship of the strap to the drum can be effected by means of the nuts 23 and 24 and the tension of the spring 25 can be varied by means of the nut 22. The lever 8 is movable about a fulcrum 32 which is in contact with the base of the casing 9.

The unit as assembled is shown clearly inFIG. 1 albeit in a slightly diagrammatic form. The spacing of the strap from the periphery of the drum must be sufficiently controlled so that when the drum is turning in the normal operation direction, in this case clockwise, the strap in no way interferes with such movement. However, on reverse movement of the shaft 5, as may happen, for example, when a conveyor belt starts moving backwards, the strap must be urged into firm contact with the drum so as to prevent a runaway in the reverse direction.

This is achieved in the hold back of the invention by filling the chamber with oil which penetrates between the strap and the periphery of the drum. On normal rotary movement of the drum in an anti-clockwise direction, the viscous and other qualities of the oil tend to transfer the rotary movement of the drum into a component of movement of the strap also in an clockwise direction. With this movement the strap tends to open up thereby allowing free rotation of the drum in the oil bath.

On reverse movement of the drum in a clockwise direction the qualities of the oil transmit to the strap an urge to move likewise in a clockwise direction. The result is that the pivot point established through the pin 15a, 15b, is forced upwards as the lever end is pulled upwards by the strap section 6 which is trying to move in a clockwise direction.

In moving upwards, the pin a, 15b urges the strap section 7 into firm braking engagement with the periphery of the drum and the drum and shaft are immediately brought to a standstill. Greater efficiency in operation is obtained by the provision of axially disposed grooves 33 in the strap sections 6 and 7 which permit excess oil to escape from the zone between the drum and the strap.

Tests have shown that immediate braking may be achieved through employment of the device of the invention and that the load is substantially equally distributed over the contact surface between the drum and the strap. Clearly, the area of contact is vastly greater than anything which may be achieved within the sphere of practical possibilities with the roller type of hold back where a plurality of line contacts is all that can be hoped for. Furthermore, in bringing the shaft to rest there is no free movement permitted to the shaft as is the case with the rack and pawl arrangement where the pawl has a whole tooth pitch to traverse before engaging a tooth on the rack wheel. Indeed, the slight interval involved where the pawl slips from the crest of one tooth en route to engaging with the next succeeding tooth can result in the development of forces sufficient to strip the rack teeth.

Many more examples of the invention exist, each differing from the other in matters of detail but in no way departing from the principles of the invention as set out in the claims which follow.

I claim:

1. A hold back" device comprising a rotatable drum; a strap substantially encircling the periphery of the drum; a lever movable about a fulcrum located towards one end thereof the other end of the lever being pivotally connected to one end of the strap; an operative connection whereby movement of the lever is transmitted to the other end of the strap to urge the latter into or out of engagement with the drum to tighten or loosen the strap and a chamber housing the several elements and defining a bath for an oil type liquid; the arrangement being such that normal rotational movement of the drum in one direction acts through the liquid disposed between the drum and the strap to urge the strap to an open position in which it does not obstruct movement of the drum, while rotational movement of the drum in the reverse direction acts through the liquid to urge the lever to move about its fulcrum to lock the drum.

2. A hold back device according to claim 1 in which the internal drum engaging surfaces of the strap include axially disposed grooves to permit the escape of liquid as braking engagement takes place.

3. A hold back device comprising a rotatable drum; a strap substantially encircling the periphery of the drum; a lever movable about a fulcrum located in a zone intermediate its ends, one end of the lever being pivotally connected to one end of the strap and the other end of the lever being constrained for movement within a predetermined range; an operative connection whereby movement of the lever is transmitted to the other end of the strap; and a chamber housing the sev' eral elements and defining a bath for an oil type liquid; the arrangement being such that normal rotational movement of the drum in one direction acts through the liquid disposed between the drum and the strap to urge the strap to an open position in which it does not obstruct movement of the drum; while rotational movement of the drum in the reverse direction acts through the liquid to urge the lever to move about its fulcrum so as to draw the strap into firm braking engagement with the periphery of the drum; said strap comprising a first arcuate section which embraces part of the drum periphery, and a second arcuate section which embraces another part of the drum periphery; a pivotal connection between the two strap sections; a pivotal connection between the free extremity of the first strap section and one end of the lever; and a pressure zone in which movement of the lever about its fulcrum in a direction to exert a braking force is transmitted to the free end of the second strap section to tighten the strap about the periphery of the drum. 

1. A ''''hold back'''' device comprising a rotatable drum; a strap substantially encircling the periphery of the drum; a lever movable about a fulcrum located towards one end thereof the other end of the lever being pivotally connected to one end of the strap; an operative connection whereby movement of the lever is transmitted to the other end of the strap to urge the latter into or out of engagement with the drum to tighten or loosen the strap and a chamber housing the several elements and defining a bath for an oil type liquid; the arrangement being such that normal rotational movement of the drum in one direction acts through the liquid disposed between the drum and the strap to urge the strap to an open position in which it does not obstruct movement of the drum, while rotational movement of the drum in the reverse direction acts through the liquid to urge the lever to move about its fulcrum to lock the drum.
 2. A ''''hold back'''' device according to claim 1 in which the internal drum engaging surfaces of the strap include axially disposed grooves to permit the escape of liquid as braking engagement takes place.
 3. A ''''hold back'''' device comprising a rotatable drum; a strap substantially encircling the periphery of the drum; a lever movaBle about a fulcrum located in a zone intermediate its ends, one end of the lever being pivotally connected to one end of the strap and the other end of the lever being constrained for movement within a predetermined range; an operative connection whereby movement of the lever is transmitted to the other end of the strap; and a chamber housing the several elements and defining a bath for an oil type liquid; the arrangement being such that normal rotational movement of the drum in one direction acts through the liquid disposed between the drum and the strap to urge the strap to an open position in which it does not obstruct movement of the drum; while rotational movement of the drum in the reverse direction acts through the liquid to urge the lever to move about its fulcrum so as to draw the strap into firm braking engagement with the periphery of the drum; said strap comprising a first arcuate section which embraces part of the drum periphery, and a second arcuate section which embraces another part of the drum periphery; a pivotal connection between the two strap sections; a pivotal connection between the free extremity of the first strap section and one end of the lever; and a pressure zone in which movement of the lever about its fulcrum in a direction to exert a braking force is transmitted to the free end of the second strap section to tighten the strap about the periphery of the drum. 